I had the same problem with my group. What I did was showing them a flashcard and elict the word, and they had to repeat it aloud three times. Don't expect children to respond very quickly, some take longer, some won't speak and some will speak a lot.
Don't give them long sentences. Stick to simple things like: I am Mary. Or: I like apples.
Once I did this activity that helped a lot: I was teaching emotions and colours, so I got hold of a bunch of different colored balloons and drew faces on them. Ss had to kick the balloon in the air and shout the color and emotion, for example: happy red balloon, sad yellow balloon, angry green balloon. It was lots of fun and they got a ton of practice.